Displays such as cathode ray tubes (CRTs) are well known for displaying motion pictures and other content such as graphical or textual content. A typical CRT has a screen that is coated on an inner surface with phosphorescent material arranged in a given pattern. The phosphorescent material glows when bombarded by electron beams emanating from electron guns to form a pattern corresponding to an image. In time, the glowing causes the phosphorescent material to wear, thus affecting its ability to display an image on the screen. It is desirable to have the phosphorescent material wear evenly across the entire screen so that over time the contrast and image display capabilities are uniform across the entire screen. Similar wear can occur with projection and plasma displays as well. It is equally desirable for these devices to exhibit even wear of the materials that facilitate their luminance.
In displays, for example, images move frequently as in a motion picture, thus allowing various parts of the phosphorescent material on the screen to glow at different times. This has an averaging effect on the wear characteristics such that no localized area of the phosphorescent material on the screen wears more or less than an adjacent localized area. However, in other instances, displayed images may contain various stationary content such as pictures, text, graphics or other stationary content. Additionally, as in the case of text, a sharp contrast may exist between the glowing areas of the text and the adjoining areas of the screen. The stationary aspect of the image, and especially the sharp contrast combined with the stationary aspect, causes uneven phosphorescent material wear characteristics between adjacent localized areas on the screen. Damage can result to the phosphorescent screen in these areas such that images are burned into the screen leaving an undesirable permanent scar in the phosphorescent coating. As a consequence, when further images are displayed in the scarred area, the outline of the image may be blurred or the outline of the scar may remain partially or totally visible. This effect is well known in the industry as screen burn-in.
In order to address this burn-in problem, various methods have been developed. For example, in computer applications where a CRT is used as a monitor, the computer generates various screen savers which turn off the still text and replace it with moving images until the user desires to view the textual information again at which time the screen saver is removed.
U.S. Pat. No. 4,677,430 teaches a method for operating a display monitor to prevent burn-in of the screen. This patent discloses a method of imperceptibly moving displayed images by changing the temporal relationship between the information signal transmitted to the monitor and signals used to synchronize the scanning of the screen. The synchronizing signal is delayed with respect to the information signal and the delay is sequentially increased from a minimum delay to a maximum delay and then sequentially decreased back to the minimum delay over a relatively long period of time. The effect of this method is that the entire screen is shifted by a vertical displacement and/or a horizontal displacement.
U.S. Patent Application Publication Number US2001/0035874 discloses a method for reducing burn-in of a CRT that is used in closed circuit television (CCTV) applications. In these applications, text is typically overlaid on a video image, usually at the bottom of the screen. This patent application teaches a method of moving the overlaid text in a window by an amount in either the x or y-axes. This US2001/0035874 allows for textual information to be moved on the screen by inserting a blank space or moving a blank space in each character line by utilizing the character generator chip to provide blanked out portions. The method periodically changes the location of the textual information overlaid onto the video image by altering the information itself so that the information is continuously available, but does not remain in the same place for prolonged period of time thus avoiding burn-in of the textual information.
In certain applications, for example, in the transmission of music over cable television or satellite television networks, various content is typically displayed in conjunction with a broadcast music channel. In other applications, such as local display of advertising content on an in store display, or various other local broadcasts some content may remain stationary, resulting in screen burn-in. This content may include various components, such as, but not limited to, an image of the album cover, artist information, music trivia, channel title, various logos, advertising material, and various other content. Some of the content may remain relatively stationary on the screen with risk of causing burn-in. The methods developed thus far are each problematic or unusable in this application. For example, screen savers are not usable since they typically make the content temporarily unavailable or unreadable. The method utilized in U.S. Pat. No. 4,677,430 discussed above is not feasible for this application because it is undesirable and impractical to modify the synchronizing signal in order to cause shifting of the screen. The method of U.S. Patent Application Publication Number US2001/0035874 allows for textual information to be moved on the screen by inserting a blank space or moving a blank space in each character line by utilizing the character generator chip to provide blanked out portions. This method is not feasible for non-textual content that is displayed as an image in an area of the screen.
What is needed is a system and method for reducing screen burn-in of a user's display which is useful in applications where various content including but not limited to images, text, or graphics is displayed.